1. Field of the Invention
The present invention generally relates to an exposure apparatus and a method for manufacturing a device using such an exposure apparatus. In particular, though not exclusively, the present invention relates to an exposure apparatus used when manufacturing a device, such as a semiconductor device and a liquid-crystal device, by lithography, and to a method for manufacturing a device using such an exposure apparatus.
2. Description of the Related Art
In recent years, miniaturization of semiconductor devices is rapidly evolving, and the main processing technique for these semiconductor devices is photolithography. There are a variety of photolithography techniques that can be applied in order to comply with such trend of miniaturization.
One known technique is a modified illumination technique in which an optimal effective light-source distribution is formed in accordance with a pattern of a reticle (photo mask). An effective light-source distribution refers to an angular distribution of an exposure light beam incident on a wafer surface, and is a light intensity distribution of a pupil plane of a projecting optical system. An effective light-source distribution is formed by adjusting a light intensity distribution of a pupil plane (for example, a plane near an exit face of a fly-eye lens) into a desired shape. The pupil plane is substantially equivalent to a Fourier-transformation surface, in an illumination optical system, which is substantially a Fourier transformation relationship with a surface provided with a pattern of a reticle. Known examples of modified illumination are annular illumination, quadrupole illumination, and dipole illumination (for example, see Japanese Patent Laid-Open No. 11-87232 and Japanese Patent Laid-Open No. 2003-318086).
It is of high concern how the degree of accuracy (i.e. the degree of symmetry and deviation of a center of gravity) of the effective light-source distribution to be adjusted in the course of modified illumination can affect the property of a pattern image formed on the wafer.
If an effective light-source distribution is asymmetrical, this can possibly be due to an optical system for forming the effective light-source distribution being decentered from an optical axis. For example, a conical prism or a pyramidal prism can be used for providing an effective light-source distribution in the course of modified illumination. When a light beam having an axially-symmetrical intensity distribution enters the prism, if the center of gravity of the light intensity distribution is misaligned with the apex of the prism, the effective light-source distribution formed by the prism becomes unbalanced, whereby the symmetry (uniformity) of the distribution is lost. Furthermore, in a case where a zoom optical system is used as the optical system, an optical element in the zoom optical system could possibly become decentered from the optical axis when the optical element is driven. In this case, the effective light-source distribution similarly becomes unbalanced, whereby the symmetry of the distribution is lost.
As a countermeasure for restricting the effective light-source distribution from becoming asymmetrical, a technique for adjusting the effective light-source distribution has been discussed in which the prism is driven in a direction perpendicular to the optical axis while measuring the effective light-source distribution (for example, see Japanese Patent Laid-Open No. 5-217853).
However, according to the technique discussed in Japanese Patent Laid-Open No. 5-217853, it can be difficult to adjust the symmetry and the center of gravity of the effective light-source distribution individually.